Embodiments of the present invention relate to a method for forming a semiconductor device, and more particularly to an anti-fuse for a semiconductor device included in a vertical gate, and a method for forming the same.
Semiconductor devices cannot be used as memory devices when a defect or failure occurs in at least one unit cell therein during a fabrication process. The memory device having at least one failed unit cell is classified as a defective product, and results in decreased production efficiency. Therefore, a technology has been introduced for substituting a defective cell with a redundancy cell included in a memory device so as to restore the memory device, which increases the production yield and reduces production costs.
A repair task of substituting the defective cell with the redundancy cell is designed to use a redundancy row and/or a redundancy column formed in every cell array, such that the row or column including the defective memory cell is replaced with the redundancy row or redundancy column. For example, if a defective cell is detected in a test process after the fabrication process is finished, a program operation for making access to a redundancy cell with an address input to access to the defective cell is carried out in an internal circuit of the memory device. Therefore, if an address signal corresponding to a defective line used to select the defective cell is input to the memory device, a redundancy line used to select the redundancy cell is accessed instead of the defective line.
A typical repair process is designed to use a fuse. However, since the method for repairing a semiconductor device using a fuse performs the repair process on a wafer level, it cannot be applied to a packaged semiconductor device. Therefore, a new method to overcome the limitations of the above-mentioned repair method using an anti-fuse is introduced.
The method using the anti-fuse can perform a program capable of easily repairing a defective cell, even if it is included in the packaged memory device. The anti-fuse performs the opposite function to the fuse. That is, the anti-fuse starts with a high resistance and is designed to create an electrically conductive path, whereas the fuse starts with a low resistance and is designed to break an electrically conductive path. Generally, the anti-fuse is formed with a very thin dielectric material of a non-conducting amorphous material, e.g., SiO2, silicon nitride, tantalum oxide, or ONO (silicon dioxide-silicon nitride-silicon dioxide) between two electrical conductors.
In accordance with a programming operation of the anti-fuse, a predetermined voltage is applied to the anti-fuse during a sufficient period of time such that the dielectric material located between two conductors is broken down. Therefore, the two electrical conductors of the anti-fuse are in short-circuit, such that the anti-fuse has very low resistance. Accordingly, the anti-fuse becomes electrically closed in a basic status.
For example, the anti-fuse includes a gate formed over a gate insulation film, a contact plug spaced apart from the gate by a predetermined distance by a dielectric thin film, and a conductive line coupled to the contact plug. Generally, the anti-fuse is designed to operate by breakdown of the dielectric thin film by applying a high voltage to the contact plug.
However, when the dielectric thin film located at the edge of the active region is broken down, the gate insulation film between the semiconductor substrate and the gate is also ruptured. As a result, threshold voltage changes, and thus device reliability deteriorates.
In addition, when a size of a gate (for example, gate width or length) is increased so as to enhance reliability and stability of the anti-fuse, the area occupied by the anti-fuse increases in proportion to the gate size. As a result, the area occupied by the anti-fuse is increased in the entire chip area, resulting in reduction in productivity.
Moreover, the gate insulation film can be broken down between the gate and the semiconductor substrate, the gate and the semiconductor are short-circuited by breakdown of the gate insulation film, and thus reliability and stability of a device deteriorated.